1. Field of the Invention
The present invention is generally concerned with torsional damper devices of the kind comprising at least two coaxial parts disposed to rotate relative to each other within defined limits of relative angular displacement against elastic means, referred to as circumferentially acting elastic means, adapted to operate circumferentially between them over part at least of said relative angular displacement.
2. Description of the Prior Art
As is known, in an automotive vehicle a torsional damper device of this kind is normally inserted into the kinematic system extending from the motor to the axles, in order to filter out vibration likely to arise at any point along this kinematic system, and thus to procure regulated transmission of rotational torque along the system.
In practice, in order to match them to the values of torque to be transmitted, the circumferentially acting elastic means employed within a torsional damper device of this kind operate in stages, only part of them being operative for low values of torque whereas, for higher values of torque, the remaining part of the circumferentially acting elastic means in turn comes into operation, either all at once or in successive stages, adding its effects to those of the previous part.
More often than not the elastic means are helical coil springs appropriately disposed circumferentally around the axis of the assembly, all or some of these springs being located on a common circumference of the assembly, for example.
The present invention is more particularly directed to the case where to minimize if not eliminate certain noises or vibrations it is desirable for the action of those springs which are alone operative for relatively low valves of the torque to extend over a relatively great proportion of the relative angular displacement between the two coaxial parts concerned.
Specifically to match them to relatively low values of torque, these are springs of relatively low stiffness.
Thus these springs are of relatively great circumferential length and relatively low stiffness and therefore relatively sensitive to centrifugal force, the effect of which is to make them curve with their median part offset radially outboard of their ends, where they can on the other hand be appropriately retained, and this is all the more marked in that the circumference on which they are disposed is of relatively large radius.
Moreover when under load on relative anqular displacement between the coaxial parts between which they are disposed, those springs of relatively great circumferential length and relatively low stiffness also tend to become curved, by virtue of a deformation similar to the previously described deformation, because of the compressive loading applied to their ends.
Such curved deformation of the springs inevitably generates friction since the springs then bear on some part of the torsional damper device relative to which they are moving in the circumferential direction.
The resulting unwanted friction torque combines in an unpredictable manner with that procured systematically to bring about the desired damping.
For the device to operate correctly it is vital to have complete control over the friction torque at all times and in particular for this torque not to vary too much as a function, for example, of the speed and/or degree of relative angular displacement.
If the friction torque is not adequately controlled, it may obliterate the torque to be transmitted when the value of this torque is low.
It is therefore important to minimize if not to eliminate the unwanted friction torque which may arise from bending of the relatively low stiffness springs.
In French patent application No. 84 17493 tiled Nov. 16, 1984 and the copending U.S. patent application Ser. No. 796,774, filed Nov. 12, 1985 corresponding thereto, retaining means are associated with these springs for this purpose, adapted to retain them radially against the action of centrifugal force.
These means comprise, for example, fingers extending circumferentially over which are engaged the relatively low stiffness springs to be retained, said fingers being in one piece with the flanges between which the springs are circumferentially operative.
An arrangement of this kind is satisfactory for certain applications but only partially so for others, the fingers employed for a particular spring being able to have only a limited circumferential size and therefore having no option but to leave free the median part of a spring for part at least of the relative angular displacement between the coaxial parts concerned, unless they are able to pass one another circumferentially for the remaining part of such angular displacement.
Also, being in one piece with the flanges unless specific action is taken they feature edges likely to damage the associated springs prejudicing the integrity thereof.
In another embodiment also described in the above mentioned patent application the retaining means employed comprise a ring over which are engaged the relatively low stiffness springs to be retained, said ring extending annularly around the axis of the assembly and thus being common to all the springs concerned.
A ring of this kind may also prove satisfactory, especially if the springs are all of exactly the same stiffness and subject to exactly the same centrifugal force and loading, together forming a balanced assembly.
As an inevitable result of the various corresponding forces, this assembly together with the associated ring tends in use to be displaced radially in a certain direction.
It has therefore to be retained in position and in the aforementioned ponding patent application, in order to achieve this, the ring employed in keyed radially to other parts of the torsional dampet device.
Thus a ring of this kind cannot fail to generate friction where it is in contact with these parts.
Also, being disposed inside the springs, as previously, it is difficult to fit and problems may arise because the space available is limited.
Finally, the necessary radial retention arrangements imply a certain degree of complexity in respect of the parts of the torsional damper device concerned.
A general object of the present invention is an arrangement which, whilst providing a simple and effective way of radially retaining the springs in question, also makes it possible to minimize or even eliminate certain at least of the disadvantages outlined hereinabove.